1. Field of the Invention
This invention relates generally to the transmission of data via broadcast digital television signals, for example digital television signals which follow the American Television Standards Committee (ATSC) format.
2. Description of the Related Art
Starting with the first ATSC standard digital television broadcast in the late 1990's, digital television broadcasting is rapidly expanding in the United States. By the end of 2000, more than 166 digital television transmitters were in operation. The FCC has set a goal that by 2006 all television broadcasting will be on recently assigned digital channels with the analog channels being returned to the government for other applications.
Sophisticated data compression techniques and the availability of increased digital signal processing capabilities make it possible to transmit high quality audio and video information in the same bandwidth as analog channels. In the television broadcast community, the Advanced Television Systems Committee (ATSC) created both the digital television standard and the high-definition television standard to take advantage of these technological advances. These standards are often referred to as ATSC digital TV or simply ATSC. A current ATSC standard uses the amplitude modulated suppressed-carrier vestigial sideband modulation technique called VSB. The 8-VSB modulation is used in terrestrial “off air” broadcast systems and the 16-VSB modulation is proposed for higher data rate cable systems.
These standards are optimized for the broadcast of TV programming. However, the rapid expansion of digital TV broadcasting and the corresponding proliferation of digital television transmitters creates opportunities for the transmission of other types of data. Examples of other types of data include data to allow cell phones to compute their own location without the need for external processing, short messages, applications similar to those on pagers, stock quotes, web pages in text form, simple grid maps showing places of interest near a cell phone, TV programming guide, radio programming guide, bus schedules, advertisements for stores in the vicinity of the receiver, and all types of low data rate mobile-commerce information.
The television infrastructure is not always suited for these types of data. For example, the ATSC standard is geared towards a certain spectral efficiency, meaning that a certain amount of information is to be transmitted over a certain spectral bandwidth. Specifically, a bit rate which is high enough to support the broadcast of television programming must fit into the bandwidth allocated for a single television channel. With this operating requirement, a certain signal to noise ratio is required in order to successfully receive the broadcast signal. For example, the 19.2 Mbps ATSC standard broadcast data rate requires the receiver to have a threoretical signal-to-noise ratio of 15 dB.
However, other operating points may be more suitable for other types of data. For example, low data rate applications may benefit from a lower spectral efficiency but a more robust transmission. This type of signal may be recovered at much lower signal to noise ratios than required to receive digital television broadcasts, thus allowing reception in remote areas, indoors, or in locations where interference or multipath causes problems. In addition, simpler receivers may be used compared to those required to receive digital television broadcasts.
Thus, there is a need for systems and methods which can take advantage of the rapidly expanding digital TV (DTV) infrastructure, but for the transmission of data other than television programming. In particular, lower data rate transmissions which are more robust are of interest.